In an electrically insulated rail joint, magnetic flux lines tend to be concentrated across the space between the two rails, especially when the joint bars or fishplates include no metal, as in U.S. Pat. No. 3,369,752 (Youngward and Kovalchuk). The magnetic flux lines tend to attract iron and other ferromagnetic particles which may bridge the space between the rails to cause an electrical short. Usually it is then necessary to dismantle the joint in order to remove the ferromagnetic particles.
The particles primarily collect along the juncture of the rails at the undersides and at the uppersides of the rail bases. To the extent that the particles collect between the joint bars and the rails, electrical shorting can be effectively inhibited by employing an insulating end post which extends outwardly beyond the rail surfaces. The same beneficial effect has been achieved by extending the insulating end post downwardly below the undersides of the rails and outwardly beyond their toes, but this requires that there be no tie plate immediately beneath the end post. To achieve this, it would often be necessary to reposition the ties.